Observer Pattern

This walks you through implementing the classic observer pattern for event-driven pub/sub communication in JavaScript and TypeScript. You get a straightforward Observable class with subscribe, unsubscribe, and notify methods, plus a practical React example showing how to decouple event handlers from multiple listeners like loggers and toast notifications. The guidance from patterns.dev is solid on when to use this (multiple components reacting to state changes) and when to skip it (high subscriber counts or when simple callbacks would do). It mentions RxJS as the production-grade option if you need more power, but the vanilla implementation here is enough for understanding the fundamentals and handling basic decoupled communication.

skills.sh installs: 653
GitHub stars: 258
last updated: Aug 21, 2026

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Install

$ npx -y skills add patternsdev/skills --skill observer-pattern --agent claude-code

Installs into .claude/skills of the current project.

Files

With the observer pattern, we can subscribe certain objects, the observers, to another object, called the observable. Whenever an event occurs, the observable notifies all its observers!

When to Use

Use this when you need to notify multiple parts of an application about state changes or events
This is helpful for implementing event-driven, asynchronous communication between components

When NOT to Use

When the subscriber count is very high and notification performance becomes critical
When simpler callbacks or direct function calls suffice for one-to-one communication
When debugging difficulty from implicit event chains outweighs the decoupling benefit